潮流计算原理

1、LOAD FLOWWhat is the purpose of a load flow study?· To calculate bus voltage levels to compare to equipment ratings.· To calculate branch current flows to compare to equipment ratings.Are electrical engineers required to perform a load flow study?· Yes, per NEC Articles 210.19 for Bra

2、nch Circuits and 215.2 for Feeders. Both articles specify voltage drop limits.· NRC requires load flow studies to verify system performance.What are good references for engineers performing load flow studies?· IEEE Std 141-1993, IEEE Recommended Practice for Electric Power Distribution for

3、 Industrial Plants (IEEE Red Book).· IEEE Std 399-1997, IEEE Recommended Practice for Industrial and Commercial Power Systems Analysis (IEEE Brown Book).Load Models· Constant kVA Model Load kVA varies by V0 example motor running· Constant I Model Load kVA varies by V1 example ballast

4、lighting, welding· Constant Z Model Load kVA varies by V2 example motor starting, heater, capacitorSource Models· PV Voltage Controlled Bus, typical generator· PQ Nonvoltage Controlled Bus, used when studying a specific loading condition of a generator, or an induction generator.·

5、; SB Swing Bus, typical utility tieNote, load flow studies require at least one swing bus in the network. Utility ties by default, are swing buses. Fig. 1. Generator reactive capability curve.What can the you do if you do not have a Reactive Capability Curve?What direction is watt and var flow for a

6、 machine operating in lag? Lead?Fig. 2. Induction motor/generator data sheet data given as motor.Fig. 3. Induction motor/generator data sheet data given as generator.Scheduled P-Q Setpoints P and Q:P = 2237 kWS = kW/pf = 2237 / 0.90 = 2486 kVAQ = (S2 P2)1/2 = (24862 22372)1/2 = 1084 kVARCalculation

7、Method AssumptionsDescription/ConditionAssumptionPower System3-phase & balancedFrequencyConstantNeutral CurrentzeroAll LoadsKVAc, Ic, ZcAll Load SourcesPV, PQ, SBSolution MethodBus voltages not loop current equationsTo run a studyAlways check “Source ImpedanceAlways check “ExactIf the system was developed with discrete components and the demand load library was never referenced, stay on the left side. Check “1st Level Demand if BHPs were entered. Check “Connected Load if studying loads running at nameplate.If you defined loads referencing the Demand Load Library stay on